1. Field of the Invention
This invention relates to a method of making a non-crystalline semiconductor layer on a substrate, and more particularly to a non-crystalline semiconductor layer manufacturing method which is of particular utility when employed in the fabrication of a semiconductor photoelectric conversion device which may be used as a solar battery.
2. Description of the Prior Art
A semiconductor photoelectric conversion device using a non-crystalline semiconductor layer composed of amorphous or semi-amorphous semiconductor layers has now been taken notice of because the non-crystalline semiconductor layer may be formed thin, that is, the semiconductor material needed is small in amount and because the photoelectric conversion efficiency can be enhanced, as compared with a semiconductor photoelectric conversion device employing a single crystal or polycrystalline semiconductor.
The following method has heretofore been proposed for forming a non-crystalline semiconductor layer or a substrate.
The substrate is disposed in a reaction tube chamber having a gas inlet and a gas outlet, and a mixture gas including at least a semiconductor material gas and a carrier gas is introduced into the reaction chamber in a state that a gas in the reaction chamber is exhausted through the gas outlet. An electromagnetic field is applied to the mixture gas to ionize it into a plasma, thereby to deposit a semiconductor material on the substrate. In this case, the atmospheric pressure in the reaction chamber is held below 1 atm and the substrate is maintained at a temperature lower than that at which the semiconductor material deposited on the substrate is formed as a crystalline semiconductor layer, thereby to obtain a desired non-crystalline semiconductor layer on the substrate.
With the conventional method, the substrate is usually disposed in that region of the reaction chamber in which the mixture gas plasma is produced. In this case, however, it is very difficult to form the mixture gas plasma homogeneously over the entire surface of the substrate in the reaction chamber because of the plasma forming mechanism.
Accordingly, the prior art method is defective in that the non-crystalline semiconductor layer formed on the substrate has many voids and is unhomogeneous in the direction of the plane of the semiconductor layer. Further, even if non-crystalline semiconductor layers are formed concurrently and individually on a number of substrates placed in the reaction chamber, the non-crystalline semiconductor layers are inevitably subject to dispersion in property; consequently, the conventional method is incapable of mass production of non-crystalline semiconductor layers of good quality.
Moreover, in the conventional method, the electromagnetic field for ionizing the mixture gas into a plasma is usually a DC electromagnetic field or a low-frequency electromagnetic field, so that the ratio in which the mixture gas is ionized into the plasma is very low.
In addition, the conventional method employs a hydrogen gas and/or an argon gas as the carrier gas, and consequently the resulting mixture gas plasma is a hydrogen gas plasma and/or argon gas plasma. Since such a carrier gas composed of the hydrogen gas and/or argon gas is ionized by a relatively low ionizing energy into a plasma, the carrier gas plasma has only a small plasma energy. Therefore, the carrier gas plasma has substantially no or a little function of promoting the ionization of a semiconductor compound gas included in the mixture gas.
Accordingly, the conventional method is defective in that the resulting semiconductor layer contains many voids and is not homogeneous in the direction of its surface.
Besides, since the carrier gas plasma composed of the hydrogen gas plasma and/or argon gas plasma is very low in thermal conductivity, the carrier gas plasma has substantially no or a little function of making the temperature distribution of the mixture gas plasma uniform throughout the reaction chamber.
Accordingly, the conventional method is incapable of a homogeneous non-crystalline, semiconductor layer.